Ribonuclease P (RNase P) is a ribonucleoprotein particle (RNP) that functions in the processing of pre-tRNAs. While RNase P is essential and present in all cells, the structure of this RNP exhibits considerable diversity. The bacterial holoenzyme consists of a large RNA molecule and a small polypeptide. The bacterial RNase P RNA has been shown to be a ribozyme, that is, the RNA is catalytic in the absence of protein. In contrast, the holoenzyme from the budding yeast Saccharomyces cerevisiae was shown to consist of an RNA molecule and at least nine polypeptides. Activity of RNase P RNA from eucaryotes in the absence of protein has never been demonstrated. The composition of another eucaryal RNase P, that of the fission yeast Schizosaccharomyces pombe, has been predicted to be very different, consisting of an RNA molecule and a single 100 kD polypeptide. However, homologs of several of the S. cerevisiae RNase P proteins have been identified in the S pombe genome suggesting these enzymes may be more similar than initially believed. This proposal entails a more complete biochemical purification and characterization of the S. pombe RNase P. The function of the S. pombe RNase P proteins will be investigated by both biochemical reconstitution experiments and genetic deletion analysis. The purification and characterization of the S. pombe RNase P will provide groundwork for further study of the complexity of eucaryal RNase P.